U.S. patent number 6,165,366 [Application Number 09/431,650] was granted by the patent office on 2000-12-26 for process for removing mercury from industrial and clinical waste water.
This patent grant is currently assigned to ICET, Inc.. Invention is credited to Shantha Sarangapani.
United States Patent |
6,165,366 |
Sarangapani |
December 26, 2000 |
Process for removing mercury from industrial and clinical waste
water
Abstract
A process is described for the removal of mercury present at
levels of 1-5000 ppb in waste water discharged from clinical
research laboratories, industries and hospitals. The process
involves preoxidation of the influent waste water with very small
amounts of hypochlorite (16-100 ppm levels)or hydrogen peroxide, in
a pretreatment tank. The waste water is then serially filtered
through two pre filters and four carbon columns at a flow rate of 5
bedvolumes/hr. The preoxidation, prefiltration, organic removal,
heavy metals removal (second column) and polishing stages (third
and fourth) are important to achieve very low levels of mercury in
the effluent. The last three columns contain activated coconut
shell carbon impregnated with mercaptothiazoline . The three
columns of the mercaptothiazoline impregnated carbon remove mercury
and other heavy metals successively and reduce their levels in the
influent to very low levels that is well below the enforced limit
of 1 ppb. The last column could be also filled with MCT impregnated
carbon fiber. Each of the columns are topped by a 0.5 foot layer of
0.5% carbon impregnated with chlorhexidine, butyl paraben and
resorcinol monoacetate to prevent biofouling.
Inventors: |
Sarangapani; Shantha (Walpole,
MA) |
Assignee: |
ICET, Inc. (Norwood,
MA)
|
Family
ID: |
23712850 |
Appl.
No.: |
09/431,650 |
Filed: |
November 1, 1999 |
Current U.S.
Class: |
210/666; 210/694;
210/756; 210/759; 210/806; 210/807 |
Current CPC
Class: |
C02F
1/283 (20130101); C02F 1/288 (20130101); C02F
1/683 (20130101); C02F 1/722 (20130101); C02F
1/76 (20130101); C02F 2101/20 (20130101) |
Current International
Class: |
C02F
1/28 (20060101); C02F 1/68 (20060101); C02F
1/72 (20060101); C02F 1/76 (20060101); C02F
001/28 () |
Field of
Search: |
;210/756,759,694,661,806,807,335,665,666 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Simmons; David A.
Assistant Examiner: Barry; Chester T.
Attorney, Agent or Firm: Hale and Dorr LLP
Claims
What is claimed is:
1. A process for removing inorganic and organic mercury from
clinical, medical, industrial and laboratory waste waters, said
process comprising the steps of:
oxidizing the waste water with hypochlorite or hydrogen peroxide in
a mixing tank;
removing mercury from the waste water by passing the waste water
through filters including mercaptothiazoline impregnated
carbon.
2. The process for removing inorganic and organic mercury from
clinical, medical, industrial and laboratory waste water of claim 1
further comprising the step of removing solids from said waste
water by passing said waste water through at least one pre
filter.
3. The process for removing inorganic and organic mercury from
clinical, medical, industrial and laboratory waste water of claim 1
wherein said filters include mercaptothiazoline impregnated carbon
are columns.
4. The process for removing inorganic and organic mercury from
clinical, medical, industrial and laboratory waste water of claim 1
wherein said carbon is coconut shell carbon.
5. The process for removing inorganic and organic mercury from
clinical, medical, industrial and laboratory waste water of claim 3
wherein each of said columns are topped with a layer of chorexidine
impregnated carbon.
6. The process for removing inorganic and organic mercury from
clinical, medical and laboratory waste water of claim 3 wherein
each of said columns is topped with a layer of resorcinol
monoacetate impregnated carbon.
7. The process for removing inorganic and organic mercury from
clinical, medical, industrial and laboratory waste water of claim 3
wherein each of said columns is topped with a layer of butyl
paraben impregnated carbon.
8. The process for removing inorganic and organic mercury from
clinical, medical and laboratory waste water of claim 1 wherein
there are four filters and the second of said four filters is used
primarily to remove solids from the waste water.
9. The process for removing inorganic and organic mercury from
clinical, medical, industrial and laboratory waste water of claim 1
wherein there are four filters and the third and fourth of said
four filters are used primarily for polishing the waste water.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method for removal of trace mercury
from industrial waste water and more particularly to a process for
removing trace mercury from clinical and hospital waste water.
Waste water produced by hospitals and hospital-related industries
originates from many sources. Such waste water is produced by
clinical laboratories, research laboratories, medical waste
incinerators equipped with fume scrubbers and hospital
laundries.
Extremely complex and diverse waste waters are generated from a
typical clinical/research laboratory associated with a hospital.
They could contain ionic mercury and organic mercuric compounds
(Methyl mercury and /or Thimersol an organic mercury compound used
as a fixative for tissue specimens), other heavy metals, organic
chemicals, blood products, body fluids, formaldehyde, dilute
acids/bases, oxidizers, oil, grease, phosphates, detergents, wastes
from automated instrumentation, photographic imaging chemicals,
radionuclides and particulate matter. In addition they contain a
variety of bacterial flora including pathogens from humans. The
liquid waste stream from an incinerator scrubber usually has low
concentrations of organic material but contains significant
concentrations of heavy metals including mercury and particulate
matter. Typical mercury concentrations range from 2 ppb to several
hundred ppb. Such waste water volumes are anywhere from a few
hundred gallons/day to over 50,000 gallons/day depending on the
size of the institution. Currently these are discharged without any
pretreatment other than pH adjustment.
Several state and federal agencies enforce a limit of 1 .mu.g/L
(ppb) for the mercury in the discharge from these facilities.
However compliance has been difficult due to the challenge of
treating the mercury for such complex waste waters and the lack of
a cost effective and reliable technology. The US Environmental
Protection Agency has been focusing increased scrutiny on the
impact of mercury discharges into the environment. Mercury is a
bio-accumulating toxic, that poses a threat to fish and the food
chain, including human beings. It, therefore, may not be discharged
to ensure that the quality of the treated affluent and the
bio-solids that are converted into fertilizer pellets, meet
applicable state and federal regulatory limits.
It is therefore a principal object of the present invention to
provide a method for removing mercury from waste water.
It is another object of the present invention to provide a method
for removing mercury from waste water in a reliable and cost
effective manner.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with this invention a process is provided for the
removal of mercury present at levels of 1-5000 ppb in waste water
discharged from clinical research laboratories and hospitals. The
process involves preoxidation of the influent waste water with very
small amounts of hypochlorite (16-100 ppm levels), in a
pretreatment tank. Alternatively, hydrogen peroxide may be used as
it has been found to be equally effective. The waste water is then
serially filtered through two pre filters and four carbon columns
at a flow rate of 5 bedvolumes/hr. The preoxidation, prefiltration,
organic removal, heavy metals removal (second column) and polishing
stages (third and fourth) are important to achieve very low levels
of mercury in the effluent. The last three columns contain
activated coconut shell carbon The three columns of the MCT
impregnated carbon remove mercury and other heavy metals
successively and reduce their levels in the influent to very low
levels that is well below the enforced limit of 1 ppb. The last
column could be also filled with MCT impregnated carbon fiber.
Each of the columns are topped by a 0.5 foot layer of 0.5%
Chlorhexidine impregnated carbon. This prevents biofouling of the
carbon columns. Activated carbon impregnated with butyl paraben and
resorcinol monoacetate (10% on w/w basis with respect to carbon)
may also be used.
These and other objects and features of the present invention will
be more fully understood from the following detailed description
which should be read in light of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the components used to practice the
method of the present invention;
FIG. 2a is a graph showing the performance results from use of the
method of the present invention during the first week;
FIG. 2b is a graph showing the performance results from use of the
method of the present invention during weeks 2-7;
FIG. 2c is a graph showing the performance results from use of the
method of the present invention during weeks 7-8.
FIG. 3a and FIG. 3b are graphs showing the performance of results
from use of the method of the present invention using activated
carbon impregnated with resorcinol monoacetate and butyl
paraben.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with this invention a process and system are provided
for the removal of mercury present at levels of 1-5000 ppb in waste
water discharged from clinical research laboratories and
hospitals.
Referring to FIG. 1, the process of the present invention involves
preoxidation of the influent waste water with very small amounts of
hypochlorite (16-100 ppm levels), in a pretreatment tank 12.
Alternatively, hydrogen peroxide may be used as it has been found
to be equally effective. The waste water is then serially filtered
through two pre filters (a 20 micron polypropylene filter 14
followed by a 5 micron polypropylene filter 16) and four carbon
columns 18, 20, 22, 24 at a flow rate of 5 bedvolumes/hr. The last
three columns 20, 22, 24 contain activated coconut shell carbon
(with a 20.times.50S mesh size which is sold by General Carbon
Corporation, of N.J.) impregnated with 1-2% of 2-Mercaptothiazoline
(MCT) which is sold by the Sigma-Aldrich Company of St. Louis, Mo.
The three columns 20, 22, 24 of the MCT impregnated carbon remove
mercury and other heavy metals successively and reduce their levels
in the influent to very low levels that are well below the enforced
limit of 1 ppb. In a preferred embodiment, the last column is
filled with MCT impregnated carbon fiber (which is sold by American
Kynol of New York). The preoxidation, prefiltration, organic
removal, heavy metals removal (second column) and polishing stages
(third and fourth) are important to achieve very low levels of
mercury in the effluent. The first column 18 was a plain activated
carbon column and the last three columns are MCT impregnated carbon
media. This MCT impregnated carbon media has an extreme affinity
for mercury as well as other heavy metals such as lead, copper,
silver, nickel and cadmium Each of the columns are topped by a 0.5
foot layer of 0.5% Chlorhexidine (which is sold by the Sigma
Aldrich Company of St. Louis, Mo.) impregnated carbon. This
prevents biofouling of the carbon columns. Activated carbon
impregnated with butyl paraben and resorcinol monoacetate (which is
sold by Sigma-Aldrich, of Minnesota) 10% on w/w basis with respect
to carbon was also found to be effective.
The dimensions of the skid mounted unit is preferably 52"
long.times.32" wide.times.48" high. The unit is equipped with
automatic shut off mechanisms and an electrical control box. Auto
samplers are connected at various positions and samples are removed
at the end of each day.
The mercaptothiazoline is less toxic than mercaptobenzthiazole
which is also known to bind mercury. The latter is a suspected
carcinogen and therefore the use of mercaptothiazoline is
preferred. The mercaptothiazoline molecules become cross linked in
the presence of oxidozers such as very dilute bleach. This
immobilizes the MCT on the carbon.
As discussed above, the extreme complexity of the waste water and
the associated microflora makes the removal of mercury a very
challenging one. Synthetic membranes, ion-exchange materials etc.,
become easily biofouled. In addition, the presence of oxidizers
such as bleach or hydrogen peroxide affects the performance of ion
exchange resins. Carbon in this respect is quite sturdy, but is
susceptible to biofouling. By coating the carbon surface with
antimicrobials such as chlorhexidine, resorcinol monoacetate and/or
butyl paraben, as taught by the present invention, a very slow
release of these materials into the rest of the carbon column keeps
the columns free from colonization of microorganisms. The
mercaptoenzthiazoline, besides being a complexing agent for heavy
metals also provides a surface that is undesirable for
microorganisms to attach onto.
This process allows examination of the extreme complexity of the
clinical waste waters and the trace mercury levels that fluctuate
day to day. The major challenge is the biological debris and the
excessive microflora in these streams that tend to foul materials
such as membranes and ion exchange media. Significant reduction in
the concentration of copper, lead and other trace metals will also
result from the use of the process and system of the present
invention. The media is also resistant to biofouling. Earlier bench
scale studies showed that plain activated carbon did not have the
sustained capacity for mercury nor the ability to resist
biofouling. These systems can thus offer excellent performance
toward achieving compliance by removing mercury and other heavy
metals from waste waters.
A study at two hospitals in the Boston area showed the
effectiveness of this process in achieving the desired effluent
values for mercury. In addition, the biofouling of the columns was
negligible in spite of the high population of microorganisms in the
waste water. The MCT impregnated carbon was also bacteriostatic,
thus preventing colonization on its surface. The following
nonlimiting examples will further explain the disclosed
invention.
EXAMPLE 1
Mercury Removal From Clinical Waste Water From a Large Private
Hospital With Activated Granular Carbon Impregnated With
Mercaptothiazole.
Granular activated carbon (activated coconut shell carbon was
treated as follows. 24.0 gms of MCT was dissolved in 1L of 80%
commercial grade Ethanol. About 1 kilogram of the dry granular
activated carbon was soaked in this solution overnight. The next
day excess ethanol was removed by vacuum drying at a temperature of
70-90.degree. C.
This site typically stores all the clinical waste water in very
large tanks prior to neutralization. The tanks are located at the
basements of this facility and due to the presence of other
equipment such as a surgical vacuum and a host of pumps and
generators, the average temperature in the basement is typically
20-25.degree. C. As a result of such favorable temperatures and the
rich nutrients in the waters, a variety of microbes in alarming
numbers (10.sup.6 cfu/ml ) thrive in these waters. Since microbes
accumulate mercury in a variety of forms, they form very adherent
biofilms which frequently slough off causing spikes of mercury in
the influent water.
The microbiological culture identification carried out during the
pilot study showed the presence of the following species. Aeromonas
sobria, A. hydrophilia.veronii, Citrobacterfreundii, Enterobacter
cancerogens, Kluyvera ascorbata, and Klebseilla pneumoniae. Some of
these are human pathogens that originate from the human body fluids
that are analyzed in the clinical labs. Thus, the waste water is an
extremely complex stream containing a host of chemicals as
described above.
The results of the testing of the pilot unit performance over a
period of eight weeks with shutdown over the weekends are shown in
FIGS. 2a through 2c. The breaks in the plot are the weekend
days.
The data indicates that mercury was efficiently removed to below 1
ppb levels. It is noteworthy that when spikes occurred the system
handled it quite well. One large spike that occurred with an
average mercury concentration of over 300 ppb was a great concern.
It was not clear how long the concentration persisted.
EXAMPLE 2
Impregnation of Activated Carbon With Resorcinol Monoacetate and
Butyl Paraben.
100 gms of each of resorcinol monoacetate and butyl paraben are
dissolved in 1L 80% commercial grade ethanol and about 1 kilogram
of the activated coconut shell granular carbon was soaked overnight
in this solution. The ethanol was removed by drying at 70.degree.
C. This site is a research laboratory on human nutrition affiliated
the USDA with an average waste water output of about 1000-1500
gallons/day. The waste water consists of excessive amounts of fats,
proteins and the other usual chemicals as described before. The
results from these tests are shown in FIGS. 3a and 3b. This
facility also has a storage tank from which the waste water is
discharged after pH neutralization. As to the microflora, the
following species were identified: Pseudomonas putida, Pseudomonas
Xanthomonas and three types of Enterobacter species. Some mold and
yeast species were also present.
While the foregoing invention has been described with reference to
its preferred embodiments, various alterations and modifications
will occur to those skilled in the art. All such alterations and
modifications are intended to fall within the scope of the appended
claims.
* * * * *